Detachable rock drill bit



arch 17, 1953 G. ANNESLEY 2,631,824

DETACHABLE ROCK DRILL BIT Filed Dec. 28, 1949 UTE- INVENTOR.

935242] amafeg ATTOR/V'y Patented Mar. 17, 1953 UNITED STATES TENTOFFICE DETACHABLE RGCK DRILL BIT Griffith Annesley, Portland, Greg.

Application December 28, 1949, Serial No. 135,499

3 Claims. 1

This invention is a continuation-impart of my application Serial No.5,853, filed February 2, 1948, for Detachable Rock Drill Bits.

This invention relates to rock drills used in percussive drillingoperations.

An object of the present invention is to provide a drill bit having astructure which results in substantially longer wear of the bit inoperation.

Another object is to provide an efficient and durable bit capable ofbeing manufactured inexpensively by quantity production methods and atsuch relatively low cost that it may be advantageously discarded afterit becomes incapable of further profitable operation.

Another object is to provide a drill rod and bit which may be readilyand securely united together while maintaining maximum efficiency of thedrill in operation.

The invention will be described with reference to the accompanyingdrawing, in which:

Figure 1 is a side elevation of a drill rod and drill bit made inaccordance with my invention and in positions to be united;

Fig. 2 is a top plan view of the drill bit;

Fig. 3 is a bottom plan view of the drill rod;

Fig. 4 is a view similar to Figure 1 showing the drill rod and bitsecurely united and with fragments broken away for convenience ofillustration;

Fig. 5 is a bottom plan view of the drill bit;

Fig. 6 is a fragmentary side elevation of a drill rod of quarter-octagonformation turned at one of its ends to a diameter slightly greater thanthe inside diameter of the socket;

Fig. 7 is an end elevation of Fig. 6;

Fig. 8 is a fragmentary side elevation similar to Fig. 6 showing thedrill rod made of hexagonal material;

Fig. 9 is an end elevation of Fig. 8;

Fig. 10 is an enlarged side elevation of the bit and drill rod unitedand with fragments broken away and indicating zones of hardness of thebit diminishing upwardly from the cutting head; and

Fig. 11 is a top plan view of a modified form of socket andcorrespondingly shaped drill rod (in section) united therewith.

Referring now more particularly to the drawing: The drill bit generallyindicated at I is provided with a cutting head 2 formed with bluntcutting or linear impact surfaces 3 which have an effective width ofless than three-thirty seconds of an inch as shown at 4. I have foundthis dimension to be critical in order to eliminate 2 excess stresseswhich frequently cause cracking or checking during the hardeningoperation caused by the small mass of the extremitywhich is subject tomuch more rapid cooling than the more remote portions of the cuttingedge 'approximately three-thirty seconds of an inch back from theintersection of planes coincident with the sides of the cutting faces.Furthermore, after fully hardening, sharp cutting edges are liable tobreak off or chip especially at the corners when in contact with hardrock, unless drawn back to approximately 62 RC, whereas, the blunt edgesas set forth in the structure of my invention may be hardened toapproximately 6! RC without fear of breaking under similar conditionswithout the necessity of being drawn back as the blunt cutting edgesalford adequate mass both to insure against cracks or checks duringhardening and breakage or chipping when in contact with hard rock. Theblunt cutting edges may be formed on a small radius preferably underthree-thirty seconds of an inch or by means of a small flat not widerthan threethirty seconds of an inch, nor narrower than one-thirty secondof an inch. Extending upwardly from the cutting head is a tapered orcylindrical socket '5 having substantially cylindrical inside walls 5and a fiat bottom wall 1. During the manufacture of the inside socket aperfectly cylindrical straight sided punch-is used to form a parallelwalled hole. However, during the heat treatment of the cutting head ofthe bit a certain amount of shrinkage occurs in consequence of which thenormally cylindrical walls of the hole may become very slightly tapered.This is not desired and is purely coincidental with the hardening of thebit and is only of the order of one or two thousandths of an inch forthe very small bits increasing up to several thousandths with the largerbits whose cutting heads contract more than do those of the smallerbits. The bottom wall is normally formed with an openingii which extendsthrough the cutting head and through which water and/or compressed airis blown in the conven-' tional manner to remove dust and rock particlesfrom the work being dealt with in the drilling operation, but thisopening may be at the side for use in soft ground.

The cutting surfaces 3 of the cutting head terminate in arcuate sidewalls or reaming surfaces 3A which project outwardly for a distance offrom one-sixty-fourth of an inch to threeeighths of an inch, the angleof said walls with respect to the vertical axis 'of" the bit .(known asthe reaming angle) lying within the range to 2". The reason forprojecting these arcuate reaming surfaces outward for a distance of overone-sixty-fourth of an inch and under threeeighths of an inch is toenable the reaming surfaces to maintain a substantially constant areathroughout the duration of their gauge reduction until such projectionsare finally worn ofi to the extent that they no longer protect theportion of the bit with or to which they are united with respect to theabrasive action of the hole. This permits an immediate or considerableextension of the reaming surfaces with consequently greatly increasedrotational friction re-' sulting in cessation of drilling within a fewseconds.

The reason for holding the reaming surfaces at an angle less than 2 isto eliminate excessive reduction in gauge diameter as it will berealized that the more acute the angle of the reaming surface thegreater will be the reduction in gauge diameter as there iscorrespondingly less metal to be removed with the acute angle than wouldbe from an angle that is almost parallel. The improved constructionincreases the strength of the corner of the bit over that which would bepossible with bits having reaming edges of over 2 and especially withbits having the normal reaming surface angle of 5 or 7 It is important,in order to achieve the long wearing qualities of the bit in accordancewith the invention, to provide such reaming surfaces with dimensionswithin clearly defined limits, in combination with the reaming anglereferred to above. Thus, the height of each reaming surface should notexceed a maximum dimension of onehalf of an inch, and the width of suchreaming surface should not exceed a maximum dimension of nine-sixteenthsof an inch. Each cutting face tapers inwardly from the top of itsreaming surface, as indicated at 3B. The angle of such tapered surface313 should be more than 45 but less than 90, and is preferably 60, withrespect to the vertical axis of the bit. In other words the reamingsurface merges into the body of the bit at a sharply sloping angle.

I have found by extended research that the short and narrow reamingsurfaces described joined by a flat sharply sloping buttress to the bodyof the bit allows further penetration without binding in a hole than canbe obtained by bits of conventional design heretofore known in the art.Thus, the reason for holding the height of the projecting reamingsurfaces below one-half of an inch and for having said reaming surfaceslope sharply towards the body, is to insure that when the reaming edgesand cutting faces wear during use the reaming edges can never exceedtheir original height, thus precluding the possibility of binding in thedrilled hole, which in turn prevents rotation and stops drilling beforethe bit is actually worn out and the full useful life obtainedtherefrom, as is the case with conventional design. During drillinggauge wear is approximately six times as rapid as cutting face wear, sothat with a shoulder angles of less than 45 with the vertical axis ofthe drill, the height of the reaming surface becomes rapidly greater,thus causing binding in the drilled hole with stoppage of rotation andcessation of drilling upon the height of the reaming surface exceedingonehalf of an inch.

The reason for restricting the effective width of the reaming edgesbelow nine-sixteenths of an inch is to allow maximum space for thecuttings to be discharged and to prevent excessive contact area with thewalls of the hole thus minimizing rotational friction and allowingsmaller machines to be used with larger bits than they would be normallycapable of rotating.

The drill rod in any of the forms shown, and generally indicated at 9 inFigs. 1 and 4, is of a diameter, as at [0, slightly greater than theinside diameter of the socket 5, and the lowermost end of the drill rodis slightly reduced or tapered as at H to a lesser diameter tofacilitate the initial introduction of the drill rod into the socketpreparatory to forcibly uniting the drill bit with the drill rod.

In accordance with a further feature of the invention, the drill bit ishardened in its entirety in varying degrees ranging, from a maximum of67 Rockwell C at the cutting head diminishing to approximately 40Rockwell C in the proximity of the mergence of the cutting head with thebase portion of the socket, then further and gradually diminishing toapproximately 33 Rockwell C at the open end of the socket. Theseblending zones of hardness have been calculated and located to renderthe socket walls radially deformable within critical limits intocylindrical zones of unlike diameters upon the forcible entry of thedrill rod. This limited deformation causes the walls of the socket toadhere in parallel relationship throughout the major portion of theirlength to the drill rod above the said tapered end thereof, and flareoutwardly to a slight degree only at their upper or open end in thelesser hardened area.

The zones of hardness are illustrated diagrammatically in the bit shownin Fig. 10. This hardening procedure makes it possible to utilizemaximum hardness from the steel and at the same time maintain sufficienttoughness in the cutting or impact surfaces of the bit to preventbreakage, chipping or other mutilation which would normally occur underthe severe conditions of shock and vibration to whichthe bit iscontinuously subjected. The bit is heat treated to produce a straightzone of Martensite laterally within the impact surface and approximatelythree-sixteenths of an inch from their extremities. This is entirelydifferent from customary practice of allowing the hardness zone to curveup the outside reaming surfaces so that the said reaming surface is ashard as the cutting faces of the bit. Indeed, with customary methods ofhardening used it is impossible not to obtain this characteristic, asadequate control cannot be exercised; The reason that I desire thisstratification of hardened zones, as clearly shown in Fig. 10, is tosecure an extremely hard, unyielding cutting face averaging 67 RockwellC for a predetermined depth to resist wear and abrasion. Immediatelyadjacent the cutting faces of the bit I obtain a zone of secondaryhardness due to the prolonging of the hardening time curve. Thissecondary zone approximates 5O Rockwell C in hardness and is designedto'provide a reasonably hard and tough backing for the primary zonedescribed hereinbefore. As will be seen from Fig. 10, the primary "andsecondary zones extend for approximatelythe full heighth of theprojecting reaming surface, each zone occupying approximately one-halfof said heighth. Upon wear taking place on each of the said reamingsurfaces, the corners are subjected to the greatest amount of wear andabrasion, and with a conventionally heat treated bit this results in thegradual formation of a tapered reaming surface which before longprevents the continuation of drilling. With my method of hardening, thecorner with its approximate hardness of 67 Rockwell C wears in thenormal way, but that portion of the reaming surface immediately above itbeing approximately 1'? points (on the Rockwell C scale) lower inhardness and consequently proportionally in wear resistance, recedesinwardly in direct proportion to the recedence of the primary zone, thustending to maintain at all times substantially parallel reaming surfaceswhich will continue to drill as their diameter becomes reduced untileventually they are no longer projected reaming surfaces, after whichoccurrence drilling ceases almost immediately.

Although the invention has been described by making a fully detailedreference to the certain presently preferred embodiments, such detail ofdescription is to be understood in an instructive rather than a limitingsense, many changes being possible within the spirit and scope of theclaims hereto appended.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. A percussive drill bit comprising in combination a substantiallycylindrical bit body, a socket formed in the upper portion of said body,a cutting head formed by a plurality of V-shaped wings having a maximumheight of one-half an inch and a maximum width of nine-sixteenths of aninch and extending radially outwards from the lowest portion of saidbody for a distance not exceeding three-eighths of an inch, said wingsterminating in arcuate peripheral end reaming surfaces, flattened impactcutting surfaces having a width of the order of three-thirtyseconds ofan inch formed on the apex of each wing and extending transversely tothe axis of the bit, said arcuate peripheral reaming surfaces slopingupwards and inwards from said flattened cutting surface at an angle ofthe order of 2 to the axis of the bit, and shoulders above said reamingsurfaces extending from the top edge of each reaming surface to theexternal surface of said socket and sloping inwards at an angle lyingwithin the range of 45 to 90 with respect to the vertical axis of thebit, said wings having a hardness varying in degrees ranging from amaximum of 6'7 Rockwell C at the impact cutting surfaces of the cuttinghead and diminishing to approximately 40 Rockwell C in the proximity ofthe mergence of the cutting head with the base portion of the socket andthen further gradually diminishing to approximately 33 Rockwell C at theupper portion of the body of the socket.

2. A percussive drill bit comprising in combination a substantiallycylindrical bit body, a socket formed in the upper portion of said body,a cutting head formed by a plurality of the V- shaped wings having amaximum radial projec- 6 tion from the cutting head. not exceedingthreeeighths of an inch and terminating in arcuate peripheral endreaming surfaces not exceeding a height of one-half inch and notexceeding a maximum width of nine-sixteenths of an inch, said wingsterminating in flattened impact cutting surface having a width of theorder of threethirty-seconds of an inch and a hardness varying from amaximum of 67 Rockwell C at the impact cutting surfaces of the cuttinghead and gradually diminishing to approximately 40 Rockwell C in theproximity of the mergence of the cutting head with the base portion ofthe socket.

3. A percussive drill bit comprising in combination a substantiallycylindrical bit body, a socket formed in the upper portion of said body,a cutting head formed by a plurality of V-shaped wings having a maximumheight of one-half an inch and a maximum width of nine-sixteenths of aninch and extending radially outwards from the lowest portion from saidbody for a distance not exceeding three-eighths of an inch, said wingsterminating in arcuate peripheral end reaming surfaces, flattened impactcutting surfaces having a width of the order of three-thirty-seconds ofan inch formed on the apex of each wing and extending transversely tothe axis of the bit, said arcuate peripheral reaming surfaces slopingupwards and inwards with respect to said flattened cutting surface, andshoulders disposed above said reaming surfaces and sloping inwards withrespect to the vertical axis of the bit from the top edge of eachreaming surface to the external surface of said socket on an angle lyingwithin the range of 45 to with respect to the vertical axis of the bit,said wings having a hardness varying in degrees ranging from a maximumof 67 Rockwell C at the impact cutting surfaces of the cutting head anddiminishing to approximately 40 Rockwell C in the proximity of themergence of the cutting head with the base portion of the socket andthen further gradually diminishing to approximately 33 Rockwell C at theupper portion of the body of the socket.

GRIFFITH ANNESLEY.

Name Date Annesley Aug. 1, 1944 OTHER REFERENCES Some New Ideas in RockBit Design, by T. M. Waterland et a1. Transactions of the CanadianInstitute of Mining, Volume XLIX, 1946, pages 123-129.

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